510 GEOGRAPHICAL ZOOLOGY. [part iv 



Family 12.— LITTORINID^. (9 Genera, 310 Species.) 



Distribution. — The Littorinidae are mostly found on the coasts 

 in shallow water ; as the common Periwinkle {Littorina littorea). 

 They are of world-wide distribution ; but Solarium and Phorus 

 are tropical ; while Lacuna, Skenea, and most species of Rissoa 

 are Northern, About 180 species are fossil, ranging from the 

 Permian to the Pliocene formations. 



Family 13.-PALUDINID^. (4 Genera, 217 Species.) 



Distribution. — The Paludinidse, or Eiver-snails, are all fresh- 

 water, and range over the whole world. Paludina (60 sp.), is 

 confined to the Northern Hemisphere ; Amjmllaria- (136 sp.), 

 is tropical ; Amphihola (3 sp.), inhabits New Zealand and the 

 Pacific Islands ; Valvata (18 sp.), North America and Britain. 

 There are 72 fossil species of Paludina and Valvata, in the 

 Wealden formation and more recent fresh- water deposits. 



Family 14.— NEPJTID^. (10 Genera, 320 Species.) 



Distribution. — All warm seas, ranging north to Norway and 

 the Caspian Sea. Neritina and Navicella inhabit fresh or brack- 

 ish waters, the latter confined to the countries bordering the 

 Indian Ocean and the islands of the Pacific. There are 80 fossil 

 species, from the Trias, Lias, and Eocene formations down to 

 recent deposits. 



Family 15.— TUEBINID^. (10 Genera, 425 Species). 



Distribution. — The genus Trochus (200 sp.) has a world-wide 

 range, but the other genera are mostly tropical, and are most 

 abundant in the Indian and Pacific Oceans. There are more 

 than 900 fossil species, found in all parts of the world, from the 

 Lower Silurian to the Tertiarv formations. 



